1. Technical Fields
Related technical fields include apparatuses, methods, and programs that recognize the position of a vehicle.
2. Description of the Related Art
Technologies for displaying the position of the vehicle and providing guidance along a route to a destination by using road-map data corresponding to actual roads are known. The road-map data includes road-network data including data on a combination of nodes and links. Usually, the node data is coordinates indicating an intersection of roads, a corner, and the like. The link data is represents links connecting the nodes to each other. Consequently, a road network showing roads based on connection relationships between plural links is achieved. Each of the links is provided with link information representing the attributes thereof. The attributes denote, for example, the link number, the coordinates of each of a start-point node and an end-point node, the link length, the type of a road, the road width, traffic regulation, and the like.
The navigation apparatus acquires information about the position of the vehicle by performing satellite navigation using a global-positioning system (GPS), autonomous navigation using an on-vehicle sensor, and the like, and identifies the vehicle position on the road-map data. However, when the vehicle travels on a narrow-angle-branch road (i.e., a road that is branched out at a relatively small angle), the vehicle-position data is often misidentified as being on a road different from the narrow-angle-branch road. This misidentification can be due to an error of the satellite navigation and/or the autonomous navigation. In the navigation apparatus, the vehicle misidentified vehicle position is superimposed and displayed on the road-map data. However, when the displayed road-map data shows a position different from the actual position of the vehicle, the driver of the vehicle can become confused.
Japanese Unexamined Patent Application Publication No. 2005-292082 (see, e.g., paragraphs [0002]-[0012]), erroneous mapping caused due to the position-measurement error can be reduced through the use of a high-precision position measurement unit that is under study, so as to be introduced in the future. Further, Japanese Unexamined Patent Application Publication No. 2006-017644 (see, e.g., paragraphs [0016]-[0024]) discloses a navigation apparatus configured to determine which of branched roads the vehicle currently travels based on a threshold vehicle speed determined based on the speed limit of a branch route and/or the state of a turn signal used to make a lane change.
When data on a destination is transmitted to known navigation apparatuses, the route of the vehicle is calculated based on the destination data so that guidance to the destination can be easily provided. On the other hand, when the destination data is not transmitted, data on a virtual target area is calculated based on the travel of the vehicle and the information corresponding to a route to the virtual target area is provided. If a road contains a branch, it becomes difficult to predict the virtual target area ahead of the branch in the road. Japanese Unexamined Patent Application Publication No. 2006-284254 (see, e.g., paragraphs [0002]-[0007] and [0043]-[0059]) proposes a course-prediction method used to predict and provide a course leaving a branch based on the travel history of a driver at the branch.